Ground maintenance vehicles for performing a variety of tasks are known. For instance, vehicles designed for (or having attachments useful for) mowing, fertilizing, aerating, detaching, vacuuming/blowing, and the like are available. While the present invention is applicable to most any such vehicle or, for that matter, to most any type of riding or walk-behind vehicle, it will, for the sake of brevity, be described with respect to riding lawn mowers.
Traditional riding mowers, e.g., those typically having four wheels wherein the front wheels are conventionally steerable, are in common use by homeowners and professionals alike. However, for professional landscape contractors and others mowing lawns having numerous obstacles, tight spaces, and/or intricate borders, mowers having zero-radius-turning (ZRT) capability are often preferred. As the name implies, “ZRT” generally indicates a vehicle having a small turning radius, i.e., a vehicle that is highly maneuverable.
ZRT riding mowers, like other ZRT vehicles, typically include a frame or chassis and at least one drive wheel located on each side (left and right) of the chassis. The drive wheels may be independently powered by a vehicle engine (e.g., via a hydraulic motor) so that, while one wheel may rotate in a first direction at a first speed, the other wheel may rotate in the same or different direction at the same or different speed. Rotating one drive wheel for forward motion while simultaneously slowing, stopping, or rotating the other drive wheel for rearward motion, may cause the mower to spin generally about a turning center located between the drive wheels, thus executing a sharp turn. Typically, the mower includes one or more other wheels, e.g., front caster wheels, in addition to the drive wheels to support the remaining weight of the mower.
While configurations vary, the drive wheels are often controlled by a twin lever control system. In this configuration, two motion control levers are typically provided and positioned side-by-side in front of the operator. Each control lever may be operatively connected to (and thus independently control) a particular drive wheel (e.g., the left lever may control the speed and direction of the left drive wheel, while the right lever may provide the same control for the right drive wheel). When the control levers are advanced forwardly in unison from a neutral position, the drive wheels may cause the mower to move forwardly in a straight line. Similarly, when the control levers are retracted in unison from the neutral position, the drive wheels may cause the mower to move in the reverse direction. Steering may be accomplished by differential movement of the control levers.
When either control lever is retracted to produce rearward movement of the mower, it may be beneficial to provide a mechanism that returns the control lever to its neutral position once the retraction force is removed. Such a feature may further provide a detectable change in required actuating force as the control lever passes through its neutral position. This function has sometimes been accomplished with, for example, a tie rod and coil spring mechanism, wherein the coil spring biases the respective lever (which is connected to the tie rod) towards the neutral position. While effective, this mechanism generally utilizes multiple components. Moreover, variability in the assembly and installation of the tie rod and spring may necessitate time-consuming adjustment of the mechanism during or after manufacturing to ensure the correct biasing force is provided.